TODO headline degeneracy cause nil string match error

[psionic-k]

* TODO
  There is no text in this headline, and TOC update will fail.  Ignoring is fine.  This is degenerate.

[alphapapa]

I don't think that ignoring the problem is a good solution. The user may expect a link to be generated, or the user may not be aware of the "dangling" heading entry.

[psionic-k]

This issue is a duplicate of #13

I've force pushed my branch to read a bit cleaner. Then I added a user warning for us to discuss.

The error was caused by attempting to do a string comparison on a nil. org-heading-components will return nil for cases demonstrated in #13

The downstream behavior in org-make-toc--link-entry-github and org-make-toc--link-entry-org correctly skips creating the link for the empty title already.

The warning reports the line for which there is no title that the downstream behavior would use to generate a link.

As a matter of style, should the warning happen in both downstream bodies, which perhaps can behave differently given that they use different link generation logic? The warning can happen at a more generic point as shown in the PR without needing to maintain both downstream link type branches. I don't believe there's a good basis for a decision in this case and will defer to opinion.

I don't believe that any other behavior such as "generating an empty link" can be a more correct way to inform the user. Generating an empty link is feedback, but it's more explicit feedback to send a warning message. Even if we do generate some other form of link, without an error message, the output is slightly confusing, partly because it won't render or behave as a link e.g. [[][]] in org mode won't render or behave.

[psionic-k]

No updates upon reread. We should finish up.